Method of treating resin impregnated fibrous webs to prevent discoloration and resulting color stabilized webs



This invention relates to methods for treating resin impregnated fibrouswebs in order to stabilize the webs against discoloration and toimproved fibrous webs obtained by such treating methods. Moreparticularly, it is concerned with (l) processes for treating textilefabrics which have thereon a permanent finish comprising a curedacetone-formaldehyde resin in order to protect the finished fabricsagainst discoloration when stored or heated subsequent to exposure tolight, and with (2) resulting treated fabrics which possess improvedcolor stability.

It is common practice in the textile industry to apply resin formingmaterials to textiles or other fibrous webs and to polymerize theapplied resin materials in situ on the webs in order to create permanentfinishes thereon which impart desired permanent effects to the webs. Oneof the important, known methods of this type for permanent finishing offabrics involves the formation of a permanent finish comprising anacetone-formaldehyde resin in the fabric. Thus, as disclosed in US.Patent 2,711,971, by applying a low molecular weight condensationproduct of acetone and formaldehyde to textiles and then subjecting theresulting materials to Suitable processing conditions to polymerize thecondensation product in situ, durable finishes providing improveddimensional stability and improved fastness to washing of mechanicaleffects, such as glazing, embossing, beetling, schreinering, pleatingand the like can be obtained, particularly with textiles which areformed of cellulosic fibers.

One of the disadvantages of textile materials finished withacetone-formaldehyde resins, is the tendency of the fabric to becomebadly discolored when stored or heated subsequent to exposure to light.The discoloration cannot then be removed by washing in water or adetergent solution such as soap and where it occurs on a printed fabricwith a substantial white area, or an unprinted fabric which is white ordyed to a pale shade, it is regarded as a serious fault.

After the textile has been heated to insolubilize the resin, it iscustomary to wash it to remove all soluble material and no matter howthorough the washing treatment given, the liability to seriousdiscoloration as a result of exposure to light followed by storage orheating, is still present. It thus appears that some substance which isactivated by light subsequently produces a highly colored compound aftera period of storage at ordinary temperatures or more rapidly at hightemperatures and that this substance is insoluble.

The tendency of acetone-formaldehyde resin finished fabrics to discoloras explained above, has seriously limited the extent of use ofacetone-formaldehyde resins in the treatment of textiles, particularlythose which are white or not highly colored. Accordingly, considerableresearch and experimentation has been devoted in the past towarddiscovering means by which this troublesome discoloration can bemitigated or completely eliminated, since the acetone-formaldehyde resinfinishes are otherwise highly attractive as textile finishing agents.

A principal object of this invention is the provision of newimprovements in the finishing of textiles or other went 0 f'dfl 41 17/77)5 Patented Aug. 3, 1965 fibrous webs with acetone-formaldehyde resinswhich eliminate the tendency of resulting webs to become discolored as aresult of exposure to light followed by storage or heating.

Another object is the provision of a method by which textiles which havea permanent finish comprising an acetone-formaldehyde resin thereon maybe treated to eliminate discoloration tendencies normally exhibited bysuch resin finished textiles without otherwise adversely affecting thedesired qualities and properties of the textile, and withoutsubstantially increasing the ultimate cost of the treated product.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description gievnhereinafter; it should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, isgiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

These objects are accomplished according to the present invention bysubjecting a fibrous web which has previously been treated to formthereon a permanent finish comprising a cured acetone-formaldehyde resinto mild oxidizing action while the web is substantially saturated withan aqueous medium, thereafter freeing the resulting web of all oxidizingmaterials and drying the web. The aftertreatment with an oxidizing agentof the fibrous webs which have been finished with acetone-formaldehyderesins in known manner operates in some fashion apparently to remove ordestroy the color forming bodies responsible for the discolorationnormally experienced in the storage or heating of this type of finishedweb after exposure to light. Consequently, the oxidizing agentafter-treatment produces finished textiles which may be stored or heatedsubsequent to exposure to light without any appreciable formation ofbrown discoloration.

After the aqueous solution having mild oxidizing action has been appliedto the fabric, the saturated fabric is subjected to time-temperatureconditions which are sufficient to obtain the desired action of removalor destruction of the color forming materials in the resin finishedfabric. The particular oxidizing agent employed and its concentration inthe aqueous medium applied to the fabric will affect thetime-temperature conditions required to produce the desired result.Using an alkaline solution containing 0.3% active hydrogen peroxide,timetemperature conditions of at least ten minutes at C. arerepresentative of conditions which can produce the desired results.

After the mild oxidation treatment, the fabric is freed of the oxidizingagent, preferably by rinsing in water, and also, where the oxidationtreatment has been carried out in the preferred manner using an alkalinesolution of the oxidizing agent, the fabric may be given a rinse in weakacid. Finally, after the fabric is thoroughly cleaned by water washingand rinsing, it is dried to obtain the final color-stable resin-finishedarticle.

A more complete understanding of the color-stabilized resin-finishedfibrous webs of this invention and the processes used for obtainingthem, may be had by reference to the following examples of actualoperations in accordance with the invention. In these examples, allparts and percentages are by weight unless otherwise specified.

Example I A low molecular weight, water-soluble, resin-formingcondensation product is prepared by reacting together one volume ofacetone and four volumes of commercial formalin containing 37% by weightof formaldehyde in the presence of 0.6 gram of sodium hydroxide, per 100cc. of reaction mixture, at a temperature about C. for about six hours.The mixture has a pH between 10 and 11 and a specific gravity of 1.04when the reaction starts. The reaction is spontaneous and as it proceedsthe mixture increases in specific gravity so that when the reaction iscompleted, a specific gravity of 1.12 is reached. At this point thereaction stops and the mixture is a syrupy solution only faintlyalkaline having a pH between 7 and 8 containing an acetone-formaldehydecondensation product of low molecular weight and having a specificgravity of 1.12.

A textile finishing bath is prepared by mixing together 224 parts of theabove prepared acetone-formaldehyde condensate, 40 parts of anhydroussodium carbonate, 5 parts of parafiin wax emulsion, 2.5 parts of atextile softening agent (Ceranine FE), 1.8 parts of a wetting agent(Lissapol N), and sufficient water to make 1060 parts.

A bleached and mercerized cotton cambric of gray construction 80 x 80,s/30s is impregnated with the aqueous treating solution by immersing thecotton fabric in the solution which is at approximately roomtemperature. The fabric is then withdrawn from the treating bath and theexcess fluid is squeezed therefrom. Next the fabric is dried and heattreated for two minutes at 143 C. and washed in water to remove solublematter.

The washed, resin-treated fabric is now subjected to a mild oxidizingaction by being immersed for ten minutes at a temperature of 80 C. in asolution containing 0.3% by weight of hydrogen peroxide and 1% by weightof sodium silicate. After this mild alkaline oxidation treatment, thefabric is rinsed, soured in weak acid, again thoroughly rinsed in waterand finally dried.

The resulting fabric, after exposure to light and storage, shows notendency to become discolored, whereas similarly treated fabric whichhas not been subjected to the mild oxidation treatment prior to exposureand storage under similar conditions, becomes markedly brown in color.

The above mentioned material Ceranine FE is a textile softening agentmarketed by Sandoz Products Limited and Lissapol N is a non-ionicwetting agent marketed by Imperial Chemical Industries Limited.

Example II A textile finishing bath is prepared by mixing together 280parts of the acetone-formaldehyde condensate as prepared in Example I,parts of anhydrous sodium carbonate, 7.5 parts of paraffin wax emulsion,2.5 parts of Ceranine FE and 1.8 parts of Lissapol N and sufiicientwater to make 1068 parts.

A bleached and mercerised cotton poplin cloth of gray construction 144 x76, 2/ 100s x 2/ 100s is impregnated by immersing in a bath of theforegoing treating solution. The cloth is then withdrawn from thetreating bath and excess liquid squeezed therefrom. Following this, thecloth is dried and then heat treated for four minutes at 132 C., afterwhich it is washed in water, rinsed in 2% acetic acid solution, andwashed in water until free from acid.

Next, the cloth is subjected to a mild oxidation aftertreatment bysteeping at 17 C. for one hour in sodium hypochlorite solutioncontaining 4 parts of available chlorine per 1000 parts of solution.Finally, the oxidation treated fabric is rinsed in water, rinsed in 2%acetic acid, again thoroughly rinsed in water and then finally dried.

There is obtained cotton poplin cloth having high dimensional stabilitybecause of the acetone-formaldehyde resin formed in the cloth and whichat the same time exhibits substantially no discoloration after exposureto light and followed by storage for several weeks. In contrast, thesame fabric treated with the resin containing impregnating solution, butnot to the mild oxidation aftertreatment, is found to acquire a verydeep brown coloration after the same exposure to light and storageconditions.

Example III A textile treating solution is prepared by mixing togetherat room temperature 224 parts of the acetoneformaldehyde condensationproduct of Example I, 40 parts of anhydrous sodium carbonate, and 1.8parts of Lissapol N and sufiicient water to make 1060 parts.

A bleached and mercerized cotton poplin of gray construction 122 x 72,36s/32s is impregnated with the solution by immersing the cotton fabricin a bath of the solution, then removing the cloth from the bath andsqueezing excess solution therefrom. This solution saturated fabric isthen dried at 93 C. and is heat treated for five minutes at 127 C. tocure the acetone-formaldehyde condensation product and permanently setit in the product. After the heat curing, the resin finished fabric iswashed in water, rinsed in 2% acetic acid at 70 C. and again washed inwater until free from acid.

A section of the fabric as prepared above is dried and is then exposedto the artificial light source of the Fadeometer for a period of timesufiicient to produce perceptible fading of the American Standard L3.The light exposed cutting is then stored in the dark for a period of sixweeks at room temperature. It is found by examination of the fabricafter such light exposure and storage that the fabric is very sronglydiscolored brown. The degree of discoloration will be greater or lesserwith increased or decreased periods of storage.

The remaining section of the resin-finished fabric, is after-treated forthirty minutes at C. in an aqueous solution containing 0.3% hydrogenperoxide, 0.5% sodium silicate, and 0.035% magnesium sulphate crystals.After this mild, alkaline, oxidation treatment, the cloth is rinsed inwater, rinsed in 2% acetic acid, again rinsed in water until free ofacid, and finally dried at room temperature.

This fabric which has been subjected to the mild oxidation treatment, isexposed to light and then stored for six weeks in the same manner as thesection of fabric not given the oxidation treatment, after which it isgiven careful examination for any evidence of discoloration. It is foundthat there is no evidence of browning or other discoloring of the fabricand it possesses an appearance substantially identical to that which itpossessed prior to the light exposure and storage. Even with increasedperiods of storage no discoloration becomes apparent.

Example IV A textile treating solution is prepared by mixing together atroom temperature 280 parts of the acetoneformaldehyde product of ExampleI, 40 parts of anhydrous sodium carbonate and 1.8 parts of Lissapol Nand sufficient water to make 1068 parts.

A bleached furnishing cotton of grey construction 52 x 40, 18s/ 75 isimpregnated with the above solution by the procedure described inExample III.

A mild alkaline oxidation solution is prepared by dissolving 5 parts ofsodium percarbonate in 1000 parts of water and heating the solution toC. The resin finished fabric as above obtained is then immersed in themild oxidation bath and held there for thirty minutes. Then, the clothis withdrawn from the bath, thoroughly washed in water, rinsed in 2%acetic acid solution, washed until free of acid, and finally dried.

After exposure to light and subsequent storage, the fabric shows nodiscoloration. In comparison, marked brown discoloration occurs on thesame resin finished fabric subjected to similar conditions of lightexposure and storage when the fabric is not given the mild oxidationtreatment as described.

The formation of a cured acetone-formaldehyde resin finish in a fibrousweb obviously constitutes the first stage of the operations contemplatedby this invention. Various forms of low molecular weightacetone-formaldehyde resin forming condensates useful in treatment andfinishing of textiles are known. The after-treatment oxidationprocedures for improvement of the color as described herein,accordingly, are contemplated for use with all fibrous webs or othertextiles which comprise a permanent finish of such acetone-formaldehydecured resins. Particularly useful in forming such resin treated fabricsare the acetone-formaldehyde precondensates formed' in aqueous medium attemperatures below 50 C. and under alkaline conditions to createproducts having a specific gravity in the range of 1.07 and 1.12 thatare stable and neutral in acid condition and contain 1 to 4 methylolgroups per mol of acetone. Further detail of the method of producingsuch resin forming condensates and the procedures used in treatingtextiles therewith can be had by reference to the aforementioned US.Patent 2,711,971.

A wide variety of oxidizing agents may be used in carrying out theafter-treatment oxidizing operations of this invention. Broadly thesuitable oxidizing agents may be classified as those which are active inneutral or alkaline aqueous solutions. Particularly useful in carryingout the oxidation procedure of the invention are those which possessuseful activity within the range pH 9-pH 11. The preferred oxidizingagents of this class include hydrogen peroxide, alkali metal peroxides,alkali metal percarbonates, alkali metal perborates, alkali metalhypochlorites, alkali metal chlorites, and alkali metal persufates,particuarly the sodium compounds. These oxidizing agents are preferredbecause they do not present any serious safety hazards, and are moreovercommonly used in the bleaching of textile materials. Thus they can besafely used upon the resin finished fabrics to produce the colorstabilization as described.

In carrying out the mild oxidation step, the fabric being treated issubstantially saturated with the aqueous solution comprising theoxidizing agent. This can be accomplished by immersing the fabric in theoxidizing solution and retaining it in the solution at the temperatureand time conditions necessary to complete the oxidation action. However,the resin finished fabric can be saturated with the oxidizing agentsolution in other ways, including spraying, padding, roller impregnatingor the like. The impregnated fabric can be pressed free of excessoxidizing agent solution and steamed or can be stored in the wet statefor a time required to allow the necessary action to take place.Similarly, the fabric may be washed in a solution of the oxidizing agentor passed through a plurality of solutions of the oxidizing agentcontained in successive tanks.

The concentration of the aqueous solution of the oxidizing agent may bevaried. Since the oxidation should be mild so as to prevent detrimentaleffects upon the fibrous structure of the web, concentrated solutionsare not recommended. The preferred concentration of the oxidizingsolution will depend to some extent upon the particular agent employed,but solutions containing between about 0.02% to 2% available oxygen havebeen found to give most desirable results. Preferably, the oxidizingagent solution should possess a pH on the alkaline side, i.e., above 7,and if the oxidizing agent upon solution in water does not provide analkaline solution, suitable alkaline agents such as alkali metalhydroxides, carbonates, silicates or the like may be added to thesolution in sufiicient amount to provide the desired alkalinity.

It is well known that the activity of many oxidizing solutions isdependent upon the pH of the solutions. This can well be illustrated byconsidering hydrogen peroxide. At a low pH, activity is low and asolution of hydrogen peroxide at pH 7 would be much too slow in reactionrate for the purpose of this invention. On the other hand, at a high pHof 12 or above, activity is so great that decomposition takes place withformation of gaseous oxygen which is thus lost and can play no usefulpart in treatment of fabrics immersed in such a bath.

It is therefore, necessary to compromise between solutions of low andhigh activity, and this is done by the addition of alkaline buffers tothe treating solution in order to provide conditions where the hydrogenperoxide will react fairly rapidly in bringing about the desiredreactions on the cloth without being so rapid that decomposition occursresulting in loss of much of the total oxidizing power of the solution.The activity of oxidizing solutions is also dependent on temperature,and here again, it is necessary to compromise between low temperatureswhere activity is very low and very high temperatures wheredecomposition to gaseous oxygen takes place.

After the saturation of the resin containing fabric with the oxidizingagent solution, sufiicient time must be allowed for the required actionby the solution to take place upon the fabric. Elevated temperaturesincrease the speed of the reaction so that shorter times are requiredwith higher treatment temperatures and vice versa. On the other hand,elevated temperatures as stated above may result in some decompositionof the active oxidizing agent. Accordingly, it is recommended that theoxidizing treatment be carried out at a temperature between about 15 andC. depending on the nature of the oxidizing agent. With the preferredoxidizing agents, times between 10 to 60 minutes are usually sufficientto obtain the necessary action in producing the color stabilization.With the mild oxidizing solutions, longer times may be used but usuallydo not produce any further improvement in results.

After the oxidation treatment, the fabric is freed of any oxidizingagent, preferably by thorough rinsing in water. This may be followed, ifdesired, by rinsing with a weak acid solution, such as a 2% acetic acidsolution, followed by a further water rinsing until the treated fabricis free of acid or other water-soluble materials. Finally, the fabric isdried and may then be employed for all uses for which resin finishtextiles are known to be useful.

The operations as above described are particularly useful for webscomprising cellulosic fibers. This includes cotton, viscose rayon, linenand the like. The invention is also effective in treatment of webscomposed partly of fibers of cellulosic origin and partly of othernatural or synthetic fibers, e.g., polyamide fibers, polyester,polyvinyl alcohol fibers, polyacrylonitrile fibers and the like. Thefibrous webs may be in the form of non-woven fabrics, woven fabrics,knitted fabrics or any other similar sheet-like material made upbasically of thread-like fibrous structures, whether in the form of atextile or other forms. No special equipment is required for applyingthe treatmg compositions or carrying out the operational steps of theinvention. Established padding or impregnation procedures may be used inthe various impregnating or saturating steps of the new methods andthese may be carried out in standard textile processing equipment.Likewise, the heating and/or drying of the fibrous webs followingsaturation with the various treatment solutions may be carried out onstandard textile handling apparatus. Furthermore, the particular fibrousweb treating operations encompassed by the invention, may, if desired,be applied in conjunction with other textile processing procedures, suchas water-proofing, calendering, embossmg, pressing and the like.Similarly, known finishing agents may be applied at suitable stages inthe new methods, and this includes application of such agents as sizingagents, softeners, lubricating materials, water-repellent agents,mothproofing agents, mildew-proofing agents, dyes, pigments and thelike.

Having provided a complete description of the invention in such manneras to distinguish it from other inventions and from what is old, andhaving provided a description of the best mode contemplated of carryingout the invention, the scope of patent protection to be granted theinvention is defined by the following claims.

We claimz= 1. A process of treating a cotton fabric finished with acured acetone-formaldehyde resin to protect the web againstdiscoloration during storage following exposure to light which comprisesimpregnating bleached cotton fabrie with an aqueous solution comprisingan acetone-formaldehyde rresin, drying the impregnated fabric, heatingthe dried fabric in air at a temperature between about 127 to 143 C. tocure the resin and set it upon the fabric, threafter immersing thefabric in an aqueous alkaline hydrogen peroxide solution containingabout 0.02 to 2.0 percent by weight of available oxygen having atemperature between about 15 and 100 C. for between about 10 to 60minutes, removing the fabric from said hydrogen peroxide solution,washing the fabric free of oxidizing material and drying the treatedfabric.

-2. A cotton fabric having thereon cured acetone-formaldehyde tresinfinish, which fabric will not discolor during storage following exposureto light, said fabric having been prepared by the process of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,267,276 12/41Hager 117-62 2,504,835 4/50 Hewett et a1. 117-161 2,507,142 5/50 Chaban260-451 2,711,971 6/55 Miller et al l17l6l 2,955,958 11/60 Brown l171132,967,787 1/61 Murphy 11762 FOREIGN PATENTS 744,093 2/56 Great Britain.

WILLIAM D. MARTIN Primary Examiner.

JOSEPH B. SPENCER, RICHARD D. NEVIUS,

Examiners.

1. A PROCESS OF TREATING A COTTOM FABIC FINISHED WITH A CUREDACETONE-FORMALDEHYDE RESIN TO PROTECT THE WEB AGAINST DISCOLORATIONDURING STORAGE FOLLOWING EXPOSURE TO LIGHT WHICH COMPRISES IMPREGNATINGBLEACHED COTTON FABRIC WITH AN AQUEOUS SOLUTION COMPRISING ANACETONE-FORMALDEHYDE RESIN, DRYING THE IMPREGNATED FABRIC HEATING THEDRIED FABRIC IN AIR AT A TEMPERATURE BETWEEN ABOUT 127* TO 143*C. TOCURE THE RESIN AND SET IT UPON THE FABRIC, THEREAFTER IMMERSING THEFABRID IN AN AQUEOSU ALKALINE HYDROGEN PEROXIDE SOLUTION CONTAININGABOUT 0.02 TO 2.0 PERCENT BY WEIGHT OF AVAILABLE OXYGEN HAVING ATEMPERATURE BETWEEN ABOUT 15* AND 100*C. FOR BETWEEN ABOUT 10 TO 60MINUTES, REMOVING THE FABRIC FROM SAID HYDROGEN PEROXIDE SOLUTION,WASHING THE FABRIC FREE OF OXIDIZING MATERIAL AND DRYING THE TREATEDFABRIC.